Improved Auto-Marking Confidence for Spoken Language Assessment

Automatic assessment of spoken language proficiency is a sought-after technology. These systems often need to handle the operating scenario where candidates have a skill level or first language which was not encountered during the training stage. For high stakes tests it is necessary for those systems to have good grading performance when the candidate is from the same population as those contained in the training set, and they should know when they are likely to perform badly in the case when the candidate is not from the same population as the ones contained in training set. This paper focuses on using Deep Density Networks to yield auto-marking confidence. Firstly, we explore the benefits of parametrising either a predictive distribution or a posterior distribution over the parameters of the model likelihood and obtaining the predictive distribution via marginalisation. Secondly, we investigate how it is possible to act on the parametrised density in order to explicitly teach the model to have low confidence in areas of the observation space where there is no training data by assigning confidence scores to artificially generated data. Lastly, we compare the capabilities of Factor Analysis, Variational Auto-Encodes, and Wasserstein Generative Adversarial Networks to generate artificial data.